Another night of potentially dangerous storms is possible in the Chicago area Friday as the threat for severe weather increases heading into the afternoon and evening hours for northern Illinois.

The flood watch is in effect until 7 a.m. Friday for Cook County, the collar counties and the majority of northern Illinois, according to the National Weather Service.

More than a month's worth of rain fell on Chicago in 90 minutes on Tuesday evening, according to the National Weather Service (NWS). "There were numerous reports of flooded viaducts, several reports of water rescues, and a few reports of flooded basements," the NWS said.

Straighter, smoother streams flow more violently than those that meander due to a reduction in friction. Areas with steeper terrain can see water accelerate downhill at a much faster rate causing a more destructive flash flood than flatter, open areas.

Friday, temperatures are expected to reach the mid 80s with a 40 percent chance of heavy rain. Saturday, the chance of thunderstorms is 50 percent with highs in the upper 80s.

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